Nerfed diseases v6 by thistleknot.

From the release notes at
http://www.bay12forums.com/smf/index.php?topic=133312.msg4804015#msg4804015

* Reduced the % chance of certain diseases considerably...

** Dwarves can now use their disease_resistance against catching the disease
   (i.e. via spreading), also the spreading is nerfed by reducing it's
   chance from 100% spreading to nearby dwarf's to a reduced % (60% for
   influenza, 25% for [visible] plagues).

** Also, resistance is used against specific applications of the diseases (i.e.
   sub syndromes of a disease, ex... necrosis of the liver is resistable).

* If a dwarf suffered from an epidemic (i.e. influenza, meningitis, or
  pnuemonia) they are immune from catching the disease for up to one
  year, does away with the need for mutations.

* Medicine now acts as a vaccine for epidemic's for one year.

* Plague Immunity (v5): Now dwarf's have a resistance chance * 2% of
  being immune to all plagues/rabies

* Medicine now has slightly extended durations against non
  communicable diseases, (i.e. blood pressure)  (needed only 3 times a
  year vs 5.22 times a year for full coverage).